From 5db8a5259c8d4bba3d99761785f2444c6b3dd5ef Mon Sep 17 00:00:00 2001
From: Keir Fraser <keir.fraser@citrix.com>
Date: Thu, 17 Dec 2009 06:27:56 +0000
Subject: [PATCH] Request re-coalescing for qcow disks. qcow driver had the
 habit of breaking each (4K) block read into 8 (512 bytes) sector reads. This
 is inefficient, but also prevents sharing detector from working, as it is
 based on page-size reads.

Signed-off-by: Grzegorz Milos <Grzegorz.Milos@citrix.com>
---
 tools/blktap2/drivers/block-qcow.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/blktap2/drivers/block-qcow.c b/tools/blktap2/drivers/block-qcow.c
index e0590ae59b..13d6c324ea 100644
--- a/tools/blktap2/drivers/block-qcow.c
+++ b/tools/blktap2/drivers/block-qcow.c
@@ -1035,6 +1035,17 @@ void tdqcow_queue_read(td_driver_t *driver, td_request_t treq)
 		}
 		
 		if(!cluster_offset) {
+            int i;
+            /* Forward entire request if possible. */
+            for(i=0; i<nb_sectors; i++)
+                if(get_cluster_offset(s, (sector+i) << 9, 0, 0, 0, 0))
+                    goto coalesce_failed;
+            treq.buf  = buf;
+            treq.sec  = sector;
+            treq.secs = nb_sectors;
+			td_forward_request(treq);
+            return;
+coalesce_failed:            
 			treq.buf  = buf;
 			treq.sec  = sector;
 			treq.secs = n;
-- 
2.30.2